Event notification constitutes a cornerstone of monitoring systems since it allows operator to capture and react to events in the network. Note that an event constitutes a significant occurrence in the system and is reported by an event notification message, also simply called notification. This notification contains information that characterizes the event itself and the context in which the event occurs. In a telecom network, an event producer is typically a managed agent and may be considered equivalent to a Network Elements (NEs). Managers typically represent the event consumers and have different demand on their agents (e.g., managers monitor agent to gather statistic related to the performance). The management entities (managers and agents) are distributed in the network.
The publish/subscribe paradigm constitutes a central enabler of event notification since it allows any NE (consumer) to expresses its monitoring demands to producers during a subscription process. As a result of this subscription process, event producers transfer to consumers the description of any event that has been triggered locally.
One of the main challenges that have to face an event system in general, and publish/subscribe event system in particular, is the load related to event notification which is put on the network elements and on Operations Support Systems (OSS). To resolve this problem, a variety of event filtering, aggregating and correlating schemes have been proposed.
In a publish/subscribe system, event filtering consists of matching an event notification against each subscription stored on the device so as to redirect this notification towards the interested consumers. Practically, the matching of an event notification against a subscription consists of verifying that the notification meets each criterion (also called constraint) defined in that subscription. If it is not the case, the event notification is not processed further, improving the system performance.
Event filtering is a costly mechanism in terms of memory usage and computation usage, since it requires going through each subscription and verifying if the attributes of the event notification meet each constraint defined in the subscription. This means that the overload increases proportionally to the number of events occurring in the network. To understand the problem with existing solutions, one has to consider two factors. The first being the cost (in term of delay and resource usage) associated with filtering a notification in which no consumer is interested is equivalent to the cost necessary to identify some interested consumers. The second factor is the amount of events raised in the managed network. This amount is often out of proportion comparing to the number of events that are relevant for one of several consumers. As a result, the majority of events that are processed during the filtering process are not relevant. Existing solutions do not provide any mechanism to identify those not-relevant events in an early stage so as to prevent from performing a costly filtering of those events and reduce the unnecessary resource usage on some nodes (network elements), which might be resource constrained, as it is the case for Radio Base Station (RBS).